An expandable jacket for the specimen of a triaxial compression test, unconfined compression test and uniaxial compressive strength tests for soils, intermediate geomaterials, soft and jointed rocks, intact rock and concrete core have been invented with the primary objective of maintaining the uniform increase of the diameter of the specimen throughout its height during the test, without forming a barrel shape or local bulging of the specimen. Since 20th century, the main criticism of these tests has been that the specimen forms a barrel shape sometimes with local bulging causing premature failure of the specimen and does not afford the accurate determination of the area of cross-section, deviator stress and shear strength.
In this invention, the expandable jacket for three-dimensional consolidation and settlement tests to determine consolidation and settlement properties of soils and intermediate geomaterials has been termed as a flexible ring. Presently, one-dimensional consolidation tests using fixed ring are performed to determine the consolidation properties in vertical direction since the 20th century, even though it has been known since that time that the consolidation and settlement of soils under a loaded area always occurs in a vertical as well as horizontal (radial) directions, i.e. in all three dimensions. In view of this, a test device using the flexible ring for determining three-dimensional consolidation and settlement properties of soils and intermediate geomaterials has been invented in this application.
The expandable jacket and flexible ring have been primarily invented for allowing uniform radial expansion of the cylindrical specimen when an axial/vertical load is applied on it. The flexible ring and expandable jacket around the cylindrical specimen comprises the segmented circular arch shaped plates around the specimen and stretchable bands or rings around the plates. The flexible ring and expandable jacket are to be installed around a specimen (generally of cylindrical shape) to perform these tests. Test preparation includes (i) installing a stretchable and impermeable membrane surrounding the specimen or surrounding the filter which surrounds the specimen, and (ii) placing a filter disk between specimen and the bottom porous disk and a filter disk between specimen and top porous disk, after which the expandable jacket or flexible ring consisting of segmented plates and stretchable bands or rings is installed surrounding the membrane. Stretchable bands or rings around the segmented plates permit uniform radial expansion to maintain uniform diameter of the specimen and apply lateral pressure on the specimen during the test.
For saturated soils and intermediate geomaterials, radial expansion of the specimen can be calculated by (i) the pore-water expelled out of the specimen and measured in a burette of control panel or (ii) by other methods such as electronic measurements by a linear variable displacement transformer (LVDT) or strain gages, or (iii) by simply assuming a value of Poisson's ratio. For partially saturated or dry soils, radial expansion of the specimen can be determined by methods (ii) or (iii) as described in the preceding sentence. To prevent bending of the LVDT probe, the LVDT is removably attached to a spring-loaded U-frame or U-frame without springs, wherein the U-frame rests on ball bearings.
The expandable jacket and flexible ring can be installed using removable attachments. For calibration of expandable jacket and flexible ring and to determine modulus of elasticity of the membrane and combined modulus of elasticity of expandable jacket and flexible ring, a calibration device is used, which comprises of a vertically movable water reservoir and a horizontal porous tube connected to a movable water reservoir or a pressure chamber as described in here-in-after.